On the nonlinear shaping mechanism for gravity wave spectrum in the atmosphere

The nonlinear mechanism of shaping of a high vertical wave number spectral tail in the field of a few discrete internal gravity waves in the atmosphere is studied in this paper. The effects of advection of fluid parcels by interacting gravity waves are taken strictly into account by calculating wave field in Lagrangian variables, and performing a variable transformation from Lagrangian to Eulerian frame. The vertical profiles and vertical wave number spectra of the Eulerian displacement field are obtained for both the case of resonant and non-resonant wave-wave interactions. The evolution of these spectra with growing parameter of nonlinearity of the internal wave field is studied and compared to that of a broad band spectrum of gravity waves with randomly independent amplitudes and phases. The calculated vertical wave number spectra of the vertical displacements or relative temperature fluctuations are found to be consistent with the observed spectra in the middle atmosphere

Observations of internal waves generated by an anticyclonic eddy: a case study in the ice edge region of the Greenland Sea

Internal waves in the ocean play an important role in turbulence generation due to wave-breaking processes and mixing of the ocean. Airborne radar images of internal waves and ocean eddies north of Svalbard suggested that ocean eddies could generate internal waves. Here, we test this hypothesis using data from a dedicated internal wave experiment in the Greenland Sea. Internal waves with dominant frequencies of 1–3 cycles per hour and amplitudes up to 15 m were observed using three thermistor chains suspended from a drifting array conveniently placed on the ice in a triangle with sides of several km. Analysis shows that internal waves propagated westwards with a speed of about 0.2 m/s and wavelength of 0.4–1.0 km, away from an anticyclonic ocean eddy located just east of the array. This was consistent with the remote-sensing observations of internal waves whose surface signature was imaged by an airborne radar in the western part of this eddy, and with theories that eddies and vortexes can directly generate internal waves. This case study supports our hypothesis that ocean eddies can be the direct sources of internal waves reported here for the first time and not only enhancing the local internal wave field by draining energy from the eddies, as studied previously. The present challenge is to explore the role of eddies as a new source in generating internal waves in the global ocean

Three-dimensional spectrum of temperature fluctuations in stably stratified atmosphere

A phenomenological model is proposed for a 3-D spectrum of temperature inhomogeneities generated by internal waves in the atmosphere. This model is a development of the theory based on the assumption that a field of Lagrangian displacements of fluid particles, induced by an ensemble of internal waves with randomly independent amplitudes and phases, is statistically stationary, homogeneous, axially symmetric in horizontal plane and Gaussian. For consistency of this model with measured spectra of temperature fluctuations in the stratosphere and mesosphere the additional assumption was introduced in to the model about the anisotropy of inhomogeneities to be dependent on their vertical sizes. The analytic expressions for both the 3-D and 1-D spectra are obtained. A model vertical wave number spectrum follows a −3 power law, whereas a horizontal spectrum contains two regions with a −3 slope, and the intermediate region with the slope between −1 and −3 depending on the rate of anisotropy decrease as a function of increasing sizes of the inhomogeneities. In the range of a few decades the model showed a good agreement with the results of measurements of the spectra in the troposphere, stratosphere and mesosphere